iOS is to iPhones what Windows is to PCs

Put another OS on it and use it for many more years

(though I don't know the status of jailbreak or alternate OSes for iPhones as my last one was a 3G and Cydia was a thriving ecosystem then)

Slap in a pair of external microphones into the lightning port and you have a pretty good field recorder with a touch screen and rechargeable battery.

Or load AUM, plug it into an audio interface with a camera connector and you have a digital mixer.

Or load Garage Band and you have a Daw in your pocket.

Setup OpenBubbles! You can iMessage from your Android.